A continuously variable transmission or CVT is a type of power transmission that is capable of infinite variability within a calibrated range of speed or torque ratios. Unlike conventionally-geared transmissions, which use a torque converter, planetary gear sets, and multiple friction clutches to establish a desired gear state, a CVT instead uses a variable-diameter pulley system. The variable-diameter pulley system, commonly referred to as a variator assembly, can transition anywhere within the calibrated range of ratios via adjustment of an applied pulley clamping pressure.
A typical variator assembly includes two variator pulleys interconnected via an endless rotatable drive element such as a drive chain or belt. The drive element rides within a variable-width gap defined by conical pulley faces. One of the variator pulleys receives input torque from a torque generating device, typically an engine via a turbine and an input gear set. The input pulley thus acts as a driving/primary pulley. The other variator pulley is connected via one or more additional gear sets to an output shaft of the CVT and thus acts as a driven/secondary pulley. Additional gear sets may be used on the input or output sides of the variator assembly depending on the configuration.
In order to vary the CVT speed or torque ratio, the clamping force noted above is applied to the variator pulleys using one or more pulley actuators. The clamping force effectively squeezes the pulley halves together in order to change the width of the gap between adjacent pulley faces. Variation in gap size, i.e., the pitch radius, causes the rotatable drive element to ride higher or lower within the gap as needed. This in turn changes the effective diameters of the variator pulleys and ultimately varies the speed or torque ratio of the CVT.